The present invention relates to a mechanism for simultaneously adjusting step support angles for the purpose of realizing a mold structure for a straight staircase.
The mechanism is of the type that includes a casing, inside of which at least two interdependent shafts are arranged in a nested configuration so that each shaft extends into the next shaft, wherein the successive intervals between the shafts are adjustable, and wherein each shaft has a threaded portion traversing an internally threaded block that is seated in the casing and holds a stair-step support.
Until now, the procedures for building mold structures for straight stairs have remained at the pre-industrial level. One starts by tracing the vertical line of each riser on the sidewalls. Next, strips of lumber are put in place on the tracing by means of nails or pins, and subsequently, the molds for the risers are attached to the lumber strips.
To make these molds is a time-consuming and therefore expensive process and requires specialized labor, without providing assurance of the quality and precision required.
To improve the technique, the U.S. Pat. No. 2,883,759 proposes a stair mold arrangement in which the mold boards are supported by a structure that extends above the staircase that is to be built.
The boards are held by arms or suspension elements that are movable and adjustable along the axis of the structure, and thus along the axis of the staircase. The arms are guided in two parallel glide rails, and a scissors mechanism allows all of the suspension arms carrying the mold boards to be moved together, whereby the interval between the support arms is automatically adjusted.
Unfortunately, an arrangement of this kind is very fragile, and the rapid wear on the scissors joints will lead to an amount of play that is incompatible with the desired level of precision.
Furthermore, the members of the scissors are often bent accidentally, which causes malfunctions that are further aggravated by the fouling of the mechanism from splashed concrete.
Moreover, a molding arrangement for a straight staircase is described in DE 1 934 586, which is designed to allow the spacing of the steps by means of a casing containing a plurality of shafts that are interdependent and can be nested, where the successive intervals between them can be adjusted. To accomplish this, each shaft has a threaded portion running through a block that is located in the casing.
With arrangements of this kind, it is not possible to arbitrarily vary the angles of the supports that determine the position of the risers (these angles vary as a function of the depth of each horizontal tread and of the height of each riser). Thus, these devices do not offer the possibility to produce any desired step configuration of a straight staircase, and they are limited by the fact that the height and depth of the steps can only be varied together, so that the use of these devices is limited to certain step configurations.